/** ***************************************************************************** * 
 * @file ModbusCRC16.c
    @author ZhongShengkeji Team
    @version V1.2.0
    @date 01-June-2019
    @brief Calculate the CRC16 value of Modbus RTU data frame
    @copyright COPYRIGHT 2019 ZhongShengkeji CO.LTD
    @taobao https://shop205432927.taobao.com
    @alibaba https://shop57528a8a66l39.1688.com
    @website www.zhongshengkeji.cn
    @phone 0769-22331829, 138 2574 1827
    @e-mail zskjdg@foxmail.com
    ***************************************************************************** */
/* Includes------------------------------------------------------------------*/ 

#include "ModbusCRC16.h"

/* Private variables----------------------------------------------------------*/
/* CRC low byte table */ 
static const unsigned char auchCRCLo[]= { 
    0x00,0xC0,0xC1,0x01,0xC3,0x03,0x02,0xC2,0xC6,0x06,
    0x07,0xC7,0x05,0xC5,0xC4,0x04,0xCC,0x0C,0x0D,0xCD, 
    0x0F,0xCF,0xCE,0x0E,0x0A,0xCA,0xCB,0x0B,0xC9,0x09, 
    0x08,0xC8,0xD8,0x18,0x19,0xD9,0x1B,0xDB,0xDA,0x1A, 
    0x1E,0xDE,0xDF,0x1F,0xDD,0x1D,0x1C,0xDC,0x14,0xD4, 
    0xD5,0x15,0xD7,0x17,0x16,0xD6,0xD2,0x12,0x13,0xD3, 
    0x11,0xD1,0xD0,0x10,0xF0,0x30,0x31,0xF1,0x33,0xF3, 
    0xF2,0x32,0x36,0xF6,0xF7,0x37,0xF5,0x35,0x34,0xF4, 
    0x3C,0xFC,0xFD,0x3D,0xFF,0x3F,0x3E,0xFE,0xFA,0x3A, 
    0x3B,0xFB,0x39,0xF9,0xF8,0x38,0x28,0xE8,0xE9,0x29, 
    0xEB,0x2B,0x2A,0xEA,0xEE,0x2E,0x2F,0xEF,0x2D,0xED, 
    0xEC,0x2C,0xE4,0x24,0x25,0xE5,0x27,0xE7,0xE6,0x26, 
    0x22,0xE2,0xE3,0x23,0xE1,0x21,0x20,0xE0,0xA0,0x60, 
    0x61,0xA1,0x63,0xA3,0xA2,0x62,0x66,0xA6,0xA7,0x67, 
    0xA5,0x65,0x64,0xA4,0x6C,0xAC,0xAD,0x6D,0xAF,0x6F, 
    0x6E,0xAE,0xAA,0x6A,0x6B,0xAB,0x69,0xA9,0xA8,0x68, 
    0x78,0xB8,0xB9,0x79,0xBB,0x7B,0x7A,0xBA,0xBE,0x7E, 
    0x7F,0xBF,0x7D,0xBD,0xBC,0x7C,0xB4,0x74,0x75,0xB5, 
    0x77,0xB7,0xB6,0x76,0x72,0xB2,0xB3,0x73,0xB1,0x71,
    0x70,0xB0,0x50,0x90,0x91,0x51,0x93,0x53,0x52,0x92, 
    0x96,0x56,0x57,0x97,0x55,0x95,0x94,0x54,0x9C,0x5C, 
    0x5D,0x9D,0x5F,0x9F,0x9E,0x5E,0x5A,0x9A,0x9B,0x5B, 
    0x99,0x59,0x58,0x98,0x88,0x48,0x49,0x89,0x4B,0x8B, 
    0x8A,0x4A,0x4E,0x8E,0x8F,0x4F,0x8D,0x4D,0x4C,0x8C, 
    0x44,0x84,0x85,0x45,0x87,0x47,0x46,0x86,0x82,0x42, 
    0x43,0x83,0x41,0x81,0x80,0x40
};

/* CRC high byte table */ 
static const unsigned char auchCRCHi[]= { 
    0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
    0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
    0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0, 
    0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40, 
    0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1, 
    0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41, 
    0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1, 
    0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
    0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
    0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40, 
    0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1, 
    0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40, 
    0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
    0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40, 
    0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0, 
    0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40, 
    0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
    0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
    0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0, 
    0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
    0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0, 
    0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40, 
    0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1, 
    0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
    0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
    0x80,0x41,0x00,0xC1,0x81,0x40 
};

/* Public functions----------------------------------------------------------*/
/** * @brief Calculate Modbus CRC16
    * @param puchMsg: Data to calculate CRC 
    * @param usMsgLen: Data length
    * @param puchCRCHi: High byte of CRC value
    * @param puchCRCLo: Low byte of CRC value
    * @note Send the low byte first 
    * @retval None
*/ 
void GetModbusCRC16(unsigned char *puchMsg, unsigned short usMsgLen, unsigned char *puchCRCLo, unsigned char *puchCRCHi) { 
    unsigned char uchCRCLo = 0xFF; 
    unsigned char uchCRCHi = 0xFF; 
    unsigned short uIndex = 0;
    
    while(usMsgLen--) { 
        uIndex = (unsigned char)(uchCRCHi^*puchMsg++); 
        uchCRCHi = (unsigned char)(uchCRCLo^auchCRCHi[uIndex]); 
        uchCRCLo = (unsigned char)(auchCRCLo[uIndex]); 
    }
    
    *puchCRCLo = uchCRCHi; 
    *puchCRCHi = uchCRCLo;
}
